The present invention relates to a system for error compensation in precision machines and measuring instruments, and in particular to a correction system for an encapsulated length measuring instrument of the type used to measure the relative position of two objects, which instrument includes a correction profile which is adjustable transversely to the measuring direction, a scale, and a scanning unit guided to move along the scale. Such instruments can be used to measure the relative positions of the slide piece with respect to the bed of a precision machine, for example.
A number of types of correction compensation systems for correcting measurement errors are known. In German Pat. No. 866 402 there is shown a measuring instrument with a correction straight edge, wherein the reading mark of the instrument is routed mechanically to a position corresponding to the respective error of a spindle opposite the scale. A similar system is shown in U.S. Pat. No. 226,162. U.S. Pat. No. 3,039,032 discloses a position measuring system which utilizes a correction template which is scanned by a sensor that acts directly on the measurement transducer. Swiss Pat. No. 266 408 discloses an optical measuring system in which a correction profile is scanned by a sensor which acts to control means for influencing the beam path of an optical reading unit. German DE AS No. 1 231 595 discloses a system for remotely displaying the movement of a movable machine component, in which a compensation system is provided for correcting measurement errors, which system comprises a deformable metal band which is scanned by a pick-up sensor. Similarly, a deformable metal band is used as a correction profile in the systems disclosed in U.S. Pat. No. 3,182,375 and U.S. Pat. No. 2,336,550. Another error correction system is described in German DE OS No. 2 042 505. There, a correction template is scanned by means of a scanning member to provide an additional movement corresponding to the previously measured error of a machine spindle in a numerical measuring system.
A number of prior art devices have provided means for adjusting correction templates. For example, in German Pat. No. 1 303 080, German Pat. No. 1 070 522, and U.S. Pat. No. 2,995,826, systems are described in which correction templates are mounted so as to be pivotable about a pivot point. By suitably orienting the correction template and then locking it in position, the effective correction profile of the correction template can be adjusted in a direction transversely to the measurement direction.
In addition, German Pat. No. 27 24 858 (which corresponds to U.S. Pat. No. 4,170,828) discloses a correction profile which is made up of a number of individual profile sections which are joined one with another so as to articulate in the manner of a chain. Individual profile sections of this device can be adjusted transversely to the measurement direction. This system provides important advantages if a correction system of great length is required due to large measuring lengths. This is because an arbitrarily large number of individual profile sections can be assembled to provide an arbitrarily long error correction system.
The error correction systems described above further include additional electrical or optical means for correcting the measuring result as a function of the correction profile, or else they are mechanically coupled to the measuring instrument. In all cases, however, they are not without problems of manufacture and assembly and they can be expensive and costly to construct.